Moisture replacement in pelletized nitrocellulose

ABSTRACT

A process of extracting water from water wet pelletized or fibrous nitrocellulose by repeatedly using a water miscible or soluble first liquid and an azeotrope forming second liquid as many times as necessary to remove a desired amount of water from the nitrocellulose is disclosed. The liquids are then recovered.

United States Patent 11 1 1111 Cox et al. 1 Dec. 9, 1975 1 MOISTURE REPLACEMENT IN 3,236,702 2/1966 Sapiego 11 149/96 PELLETIZED NITROCELLULOSE 3,251,823 5/1966 Murphy 11 149/96 3,284,253 ll/l966 Westfield.. 149/96 1 Inventors: Charles Paw W. 3,315,572 6/1967 Sapiego 149/96 Craig E. Johnson, Indian Head; 3,325,571 6/1967 Sapiego..." 149/96 Larry D. Henderson, Bryans Road, 3,346,675 10/1967 Sapiego..... 149/96 both f 3,671,515 6/1972 149/96 3,702,271 11/1972 Henderson.... 149/96 Asslgneer The Unfled States of America 88 3,723,207 3/1973 Camp 149/96 represented by the Secretary of the 3,767,489 10/1973 Reinhart 149/96 Navy, Washington, DC.

[ Filedi it- 6, 1973 Primary ExaminerHerbert B. Guynn [2 APPL Nu: 422 243 Assistant Examiner-D0nald P. Walsh Attorney, Agent, or FirmR. S. Sciascia; J. A. Cooke [52] US. Cl. 149/96; 149/2; 149/92; 149/98; 149/99; 149/100; 260/223 511 1111. cm C06B 45/00; C068 25/18; {57] ABSTRACT A process of extracting water from water wet pelletized or fibrous nitrocellulose by repeatedly using a [58] F'eld Search f water miscible or soluble first liquid and an azeotrope 149/1096 260/223 264/3 forming second liquid as many times as necessary to 198 remove a desired amount of water from the nitrocellu- [Sm References Cited lose is disclosed. The liquids.are then recovered.

UNITED STATES PATENTS 8/1965 Bergman 149/96 12 Claims, No Drawings MOISTURE REPLACEMENT IN PELLETIZED NITROCELLULOSE BACKGROUND OF THE INVENTION This invention relates to a process for preparing an explosive binder, and more specifically to a process for removing water from fibrous or pelletized water wet nitrocellulose (hereinafter NC or nitrocellulose).

From the beginning of the manufacture of double base propellants or explosives containing nitrocellulose, water in the nitrocellulose has been detrimental to the propellants or explosives. Tensile strength and stability of the propellant or explosive have suffered especially. To remove the water from the nitrocellulose, many processes have been used. The obvious way to dry is by heating. However, since dry nitrocellulose is heat sensitive careful control and observation must be used to avoid explosions while at the same time permitting the drying to continue to the desired point. Also convection air drying and vacuum drying prior to mixing with a propellant have been used. However, since the removal of water is dependent solely on the vapor pressure of water with respect to the final pressure and surface area of the fluid explosive or propellant extremely low rates of water removal are obtained thereby increasing processing time. These processes produce dry nitrocellulose and result in additional problems from a safety and a quality standpoint. The dry nitrocellulose must be carefully handled, or it will explode. Also the dry nitrocellulose is easily contami nated upon handling. Thus, it can be seen that water wet nitrocellulose has undesirable properties for use in propellants or explosives and that dry nitrocellulose is difiicult to handle.

A proposed solution to this particular problem is forming an azeotrope with the water in the nitrocellulose. Then nitrocellulose can be mixed with a propellant. The azeotrope is then evaporated, thereby removing the water. There is, however, a problem because sometimes water is reluctant to form an azeotrope. So while azeotrope formation removes water and avoids both the handling of dry nitrocellulose and the problems involved therein, there is still difficulty in removing water from nitrocellulose. Also the liquids used to remove the water are expensive and add appropriately to the cost of the process.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a process for removing water from nitrocellulose.

It is also an object of this invention to provide a process for removing water from nitrocellulose without drying such nitrocellulose.

It is a further object of this invention to provide a process for increasing tensile strength and stability of nitrocelluIose-containing propellants by removing water therefrom.

A still further object of this invention is to provide a process for treating nitrocellulose by increasing the azeotrope formation comprising first treating with an organic liquid with water in the nitrocellulose an thereby more easily remove water from the nitrocellulose.

It is also an object of this invention to provide a process for treating nitrocellulose which includes recovering and recycling the treating liquids in order to reduce costs.

It is a further object to provide a process for replacing water in the nitrocellulose with a material more suitable for making propellant or explosive compositions thereby avoiding the problems caused by the pres ence of water.

These and other objects of the invention are met by treating the waterwet nitrocellulose with a first liquid which is completely miscible with or soluble in water, which is a nonsolvent for nitrocellulose. and which is further completely miscible with or soluble in a second liquid. The second liquid is a non-solvent for nitrocellulose, is immiscible with water, and is completely miscible with, soluble in or capable of forming an azeotrope with the first liquid. Following one or more treatments with the first liquid, the nitrocellulose is treated one or more times with the second liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Nitrocellulose is commonly made and shipped in a water-wet form wherein water comprises about [0 to 40% based on the weight of the nitrocellulose. A common pelletized nitrocellulose is plastisol nitrocellulose (hereafter PNC) as described in US. Pat. No. 3,67l,5l5 to Cox et al. and US. Pat. No. 3,702,353 to Henderson et al. In the process of this invention, waterwet nitrocellulose is first treated with an organic liquid which is miscible with water or completely soluble in water. This liquid also does not dissolve the nitrocellulose. The liquid is the first liquid which is used to treat the water-wet nitrocellulose. The first liquid also forms an azeotrope with. is completely miscible with, or forms a solution with a second liquid. The second liquid treats the nitrocellulose after the first liquid has treated the water-wet nitrocellulose. However, the first liquid is still present at the time of treating with the second liquid. This second liquid forms an uzeotrope with, dis-- solves, or completely mixes with water and the first liquid. Decanting the first liquid and the second liquid from the nitrocellulose removes some water from the nitrocellulose. The adding and decanting of the first liquid and the second liquid are repeated until up to 0.5% water by weight of the nitrocellulose remains in the nitrocellulose. It is suitable to reduce the water content down to 0.2 or 0.1% by weight of the nitrocellulose. Sometimes it is even more suitable to get the water content down to or below 0.0l% by weight of the nitrocellulose. This process of treating with the first and second liquid is capable of reducing water content to that level. The second liquid which remains with the nitrocellulose is suitable for assisting in formulat ng nitrocellu lose with other materials for forming a propellant or an explosive.

A suitable first liquid is required to be miscible with water, a non solvent for nitrocellulose and capable of forming an azeotrope or a solution with the second liquid. Amounts of the first liquid used to treat the waterwet nitrocellulose depend on how many times the nitrocellulose is treated. An especially suitable first liquid is isopropanol which is a non solvent for nitrocellulose; and completely soluble in both water. and hexane or heptane. Isopropanol is especially suited for this. Meth anol, ethanol and butanol partially dissolve PNC and are unsuitable. Other alcohols may be used provided they are miscible with Water and do not dissolve PNC. The nitrocellulose may also be treated with the first liq uid more than once before the addition of the second liquid. Also the second liquid can be used to treat the nitrocellulose with or without an immediately preceding treatment with the first liquid, provided, however, that at least one treatment with the first liquid is used. For example, the first liquid may be slurried with the nitrocellulose one, two, three or more times before addition of the second liquid. Also the second liquid may be the slurrying liquid for the nitrocellulose one, two, three or more times with each slurrying not requiring a preliminary slurrying with the first liquid. However, at least one slurrying with first liquid is required before any addition of the second liquid.

The second liquid to be suitable for the purposes of this invention is required to be capable of forming an azeotrope with both water and the first liquid. The second may also form a solution with the first liquid or completely dissolve the first liquid. Lower alkyl liquids of up to carbon atoms are suitable for forming the azeotrope or dissolving the alcohol. Especially suitable materials are heptane and hexane due to their availability. Suitable amounts of the second liquid depend on how much it is desired to reduce the water content of the nitrocellulose and how many times the nitrocellulose is reslurried.

While some of the second liquid still remains in contact with the nitrocellulose it is possible to add to the nitrocellulose a wide variety of propellant or explosive components. Any of the standard organic or inorganic explosive or propellant materials can be added while the second liquid is present. Suitable propellant and explosive components include metriol trinitrate, cyclotetramethylene-tetranitramine (hereafter HMX), or cyclotrimethylene-trinitramine (RDX.). Other suitable components are disclosed in US. Pat. Nos. 3,723,207 to Camp and 3,702,271 to Henderson et al. Metriol trinitrate is especially suitable as the stabilizer which inhibits the tendency of the nitrocellulose to absorb water hygroscopically.

The liquids used to treat the water-wet nitrocellulose can easily be recovered for further use in the process at a cost savings. The water miscible first liquid is extracted from the second liquid with water. An excess of water is used which destroys the azeotrope or extracts the first liquid from the solution with the second liquid to form layers of the second liquid, and water in combination with the first liquid. Liquid layer separation is then possible to recover the second liquid. The first liquid is then separated from water by distillation.

The process is also applicable for removing moisture from fibrous NC both of a high and low nitrogen content. The advantage of the invention is that PNC or NC is never handled in the dry state and thus is considerably safer to handle. For production operation the process would be carried out continuously using slurry tanks and solid bowl centrifuge instead of the batch method described in the following example.

The following example is presented to illustrate the invention without unduly limiting the scope thereof:

EXAMPLE A quantity of 13.58 grams of 26.36% water-wet PNC was well slurried in 87.27 grams of isopropyl alcohol. This slurry was allowed to settle for 24 hours. Then 78.29 grams of isopropyl alcohol-water were decanted and 75.61 grams of new isopropyl alcohol were added. The mixture was again well slurried. After 24 hours 80.39 grams of isopropyl alcohol water were decanted. Then 72.98 grams of hexane were added and the mixture was well slurried. After 24 hours 70.16 grams of hexane-isopropyl alcohol were decanted, 72.98 grams of new hexane were added, and the mixture was well slurried. It quickly settled and four hours later 68.73

grams of hexane-isopropyl alcohol were decanted, 68.11 grams of new hexane were added and the mixture was well slurried. Twenty-four hours later 52.08 grams of hexane-isopropyl alcohol were decanted. A slurry of approximately 10 grams PNC and 26 grams hexane remained. To this were added 10.0 grams of metriol trinitrate (MTN) (moisture content determined to be 0.140%). The paste mixture was vacuum dried at 28 inch l-lg vacuum to remove the residual hexane. One (1.0) gram of this paste was mixed with 9.0 grams of MTN (moisture content deterimined to be 0.045%) to make a thin PNC-MTN paste. A Karl Fisher test was described in Military Standard No. 286, Revision B, 18 August I961, Method Number l0l.5, determined the moisture content of this paste to be 0.077%. When the water contribution by the MTN was taken into account the resulting equivalent moisture content of the PNC was found to be 0.60% which is quite adequate for slurry cast compositions that utilize PNC for the binder.

isopropyl alcohol dissolved the water entrapped in the PNC particle without solvating the PNC.

MTN was added to prevent the absorption of water by the hygroscopic nitrocellulose. Also other materials can be added.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A process for removing water from water-wet nitrocellulose comprising:

a. treating the nitrocellulose with a first liquid which is a non-solvent for the nitrocellulose and which is miscible with water to form a slurry;

b. adding to the slurry a second liquid which is a nonsolvent for the nitrocellulose and which forms an azeotrope with water and the first liquid and is miscible with the first liquid;

c. removing the first liquid and the second liquid from the slurry and an amount of water from the nitrocellulose;

d. recovering nitrocellulose containing up to 0.5% of water by weight.

2. The process of claim 1 wherein step (a) is carried out at least once before proceeding to step (b).

3. The process of claim 2 wherein steps (a), (b), and (c) are repeated sequentially until the water content is reduced to 0.2% by weight of the nitrocellulose.

4. The process of claim 2 wherein steps (b) and (c) are repeated inorder to remove a mixture of the first liquid and the water from the slurry.

5. The process of claim 4 wherein the first liquid is isopropanol.

6. The process of claim 5 wherein the second liquid is heptane or hexane.

7. The process of claim 6 wherein the recovered nitrocellulose contains up to 0.01% water.

8. The process of claim 7, wherein the nitrocellulose is fibrous.

9. The process of claim 7, wherein the nitrocellulose is pelletized.

6 The PTOCESS of claim 7 wherein the f f liquid 12. The process of claim 7 wherein after removing IS recovered from the water and the first liquid by extraction and before recovering, an explosive or propellant comll. The process of claim 10 wherein the first liquid Ponem is added to the nitrocelluloseand the water are separated by distillation. 5 

1. A PROCESS FOR REMOVING WATER FROM WATER-WET NITROCELLULOSE COMPRISING: A. TREATING THE NITROCELLULOSE WITH A FIRST LIQUID WHICH IS A NON-SOLVENT FOR THE NITROCELLULOSE AND WHICH IS MISCIBLE WITH WATER TO FORM A SLURRY; B. ADDING TO THE SLURRY A SECOND LIQUID WHICH IS A NON-SOLVENT FOR THE NITROCELLULOSE AND WHICH FORMS AN AZEOTROPE WITH WATER AND THE FIRST LIQUID AND IS MISCIBLE WITH THE FIRST LIQUID; C. REMOVING THE FIRST LIQUID AND THE SECOND LIQUID FROM THE SLURRY AND AN AMOUNT OF WATER FROM THE NITROCELLULOSE; D. RECOVERING NITROCELLULOSE CONTAINING UP TO 0.5% OF WATER BY WEIGHT.
 2. The process of claim 1 wherein step (a) is carried out at least once before proceeding to step (b).
 3. The process of claim 2 wherein steps (a), (b), and (c) are repeated sequentially until the water content is reduced to 0.2% by weight of the nitrocellulose.
 4. The process of claim 2 wherein steps (b) and (c) are repeated inorder to remove a mixture of the first liquid and the water from the slurry.
 5. The process of claim 4 wherein the first liquid is isopropanol.
 6. The process of claim 5 wherein the second liquid is heptane or hexane.
 7. The process of claim 6 wherein the recovered nitrocellulose contains up to 0.01% water.
 8. The process of claim 7, wherein the nitrocellulose is fibrous.
 9. The process of claim 7, wherein the nitrocellulose is pelletized.
 10. The process of claim 7 wherein the second liquid is recovered from the water and the first liquid by extraction.
 11. The process of claim 10 wherein the first liquid and the water are separated by distillation.
 12. The process of claim 7 wherein after removing and before recovering, an explosive or propellant component is added to the nitrocellulose. 